This invention relates to polymeric compositions having an elongated dispersed phase polymeric material disposed in another polymeric material and articles containing the compositions and methods of making and using the compositions. In addition, the invention relates to adhesive compositions having an elongated dispersed phase material disposed in an adhesive material and articles containing the compositions and methods of making and using the compositions.
Optical films and other devices have been developed for a variety of applications, including for use as decorative articles and to enhance or alter characteristics of displays. In particular, there are instances when it is desirable to anisotropically reflect or otherwise scatter light. For example, in many display and projection screen applications, a broad horizontal viewing angle is desirable because a user or viewer may be positioned to the side of the display or projection screen. On the other hand, the vertical viewing angle typically does not need to be as broad because the user or viewer is typically positioned with the display or projection screen at or near eye level. Accordingly, it can be desirable to have an anisotropic display with a relatively broad horizontal viewing angle, but a relatively narrow vertical viewing angle.
One method to modify the viewing angle includes the use of surface structure, such as a lenticular lens screen, where one dimensional lens structures are molded onto plastic substrates. Light is focused by the cylindrical-like lens structures onto a diffusive film to achieve asymmetric diffusion. However, lenticular screens contain a series of tangible grooves which can be expressed as a frequency. This frequency can interfere with the pixel frequency in liquid crystal based projection displays and generate Moire fringes. Thus, the use of current lenticular screens is limited for high definition image display in which pixel frequencies are higher.
Another issue with optical films and devices is the extraction of light from the optical film or device. A number of films and devices act as waveguides in which the light remains within the waveguide by, for example, total internal reflection due to the difference in refraction indices between the waveguide and the surrounding environment (e.g., air). Total internal reflection is used, for example, to transmit light down optical fibers with little loss in the light intensity. However, it may be desirable to extract light at various points along the waveguide (e.g., to make a sign or other display) or to overcome unwanted total internal reflection. For example, light emitting diodes, organic light emitting devices, luminescence films, and fluorescence films are produced to emit light. However, total internal reflection frustrates, at least in part, light emission except at edges. Thus, it is desirable to have a product that can facilitate the extraction of light from non-edge surfaces.
Generally, the present invention relates to polymeric compositions that can be used to anisotropically scatter light, extract light from waveguiding devices and films, or both. One embodiment is a polymeric composition that includes a first polymeric material, for example, an adhesive material, and a second polymeric material disposed as a plurality of elongated structures within the first polymeric material. Each elongated structure has a major axis and the major axes are substantially aligned. The first polymeric material has an index of refraction that differs by at least 0.01 from an index of refraction of the second polymeric material. In some instances, a pressure sensitive adhesive material is selected as the first polymeric material. The orientation of the elongated structures and the difference in indices of refraction results in the polymeric composition scattering light asymmetrically.
Another embodiment is an article that contains a substrate and the polymeric composition. This article can be used with or also include a light guide, wherein the polymeric composition is disposed on the light guide and extracts light from the light guide. In other instances, the article includes or is disposed on a display to increase a viewing angle of the display in at least one direction.
Yet another embodiment of the invention is a method of making an article. A polymeric composition is formed using a first polymeric material and a second polymeric material dispersed in the first polymeric material. An index of refraction of the first polymeric material differs by at least 0.01 from an index of refraction of the second polymeric material. The polymeric composition is then dispensed on a substrate. This dispensing results in the second polymeric material forming multiple elongated structures within the first polymeric. Each of the elongated structures has a major axis and the major axes of the elongated structures are substantially aligned.
Another embodiment of the invention is an article the includes a medium configured and arranged to contain light and a light extraction element disposed on at least a portion of the medium. The light extraction element comprises the polymeric composition described above.
The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The Figures and the detailed description which follow more particularly exemplify these embodiments.